Rough Idle on my '05 G35
 

Hey guys new user here *yay* but anyway, I have been noticing lately that my car has a rough idle. It seemed to have started a few months ago, but it only happens every once in a while.

The rough idle is very annoying, the car shakes and it feels like it is going to die on me. My normal idle is right around 650 rpm. when its rough it keeps dropping from 650 down to 450 constantly, sometimes lower when its really bad.

Car has 192K miles on it. Not ready to lose it yet...

Car drives fine, maybe slightly more sluggish than it used to be, but that may just be me.

What it feels to me like is bad gas, but since this beginning to happen more often, and I go to more than 1 gas station I dont think it is that. I always fill up with premium too.

But gas seems to go "bad" quickly in my car. I left my car sitting for about 5 days when I went on a trip one week. When I cam back the car wouldnt start, adding gas to the tank and it fired up but ran badly. Filled it up at nearest gas station, and it ran perfectly.


So does anyone have any possible solutions to my problem? I really think it has something to do with the fuel system. could be injectors, fuel pump, or some leak in the system that lets the gas go "bad" after a short period of time?? I honestly dont know, that is why I am asking here! all help is appreciated.

update: got some codes, even though there was no MIL light?

first one is P0304; cylinder 4 misfire (sort of expected this with the rough idle)

second one is P0430; catalyst system efficiency below threshold - bank 2

Keyboard diagnosis is a problem with cylinder # 4. Plug, coil pack, injector... allowing un burnt fuel to hit the cat. Can you smell any excess fuel @ the exhaust?

didnt check for that. will tommorow.

I just remembered whenever I changed the spark plugs (around 130K miles) there was oil on one of the plugs. It was either cylinder 4 or cylinder 6, I cannot remember. Could the spark plug be covered in oil, thus no spark? Or is my thinking wrong? Could the oil have affected the coil in a bad way that it stopped working? From my understanding the valve covers need to be replaced to fix this. I can do that, but as far as getting the car working now, what should I do?

I'd start by switching coil packs and see if the problem moves to the cylinder you took the "good" coil pack from. That will @ least confirm or rule out coil pack problem. Oh, and of course, pull the plug and check it's condition.

Ok today we swapped around the coil packs, still had cylinder 4 misfiring. We also changed the spark plug in that cylinder just to be sure, we used iridium so the gap is correct. We will change the rest as soon as car is working. It is still misfiring. We did a compression test to be sure it's not a major problem, and compression checked out fine. Ideas now are that it is a fuel delivery issue, whether it be injector or fuel pump I am not sure. We can smell gas out of the exhaust.

My fuel gauge doesn't work properly, so I am thinking I will change the fuel pump first. Trouble is where can I get an entire fuel pump assembly for my SEDAN? All the ones I see say they are for the coupe.

Also, do you think I should swap injectors? Do I need to swap injectors? How do I swap injectors? I know they are located under the plenum. Which injectors should I buy? Do I need to replace all of them or just one?

If you have any other ideas let me know. My spark plug cables look to be perfectly fine, though I know it could be that. They are in healthy visual condition. So I am going to assume it's not those.

Edit: I must add it only sputters (misfires) at idle. Anytime i am giving it the gas it is fine. Haven't tried driving it hard so I can't tell you that. Don't really want to lol

Next thing I'd do is verify spark by having the plug out and laying on a grounded surface while hooked to the coil pack. Have a friend crank the engine while you check for spark @ the plug. * Remove the fuel pump fuse B4 doing this*

I am not a mechanic, ( well automotive that is), just relaying what I would do if I had the same situation to deal with.

i have heard the oil from the valve covers can foul up the coil packs. as long as you are getting spark and fuel you should be ok. check your injectors and make sure the spark is going off.

ok I have verified that there is a spark by doing exactly what you said markc. hurleyguys, that could be a problem but my coil pack in cylinder 4 is actually ok. And I have verified it sparks so it is all good with the spark plugs and ignition. what do I need to do next? injectors? how can I check the injectors?

Unsure how easy it is to swap injectors, but you said that the issue seems to center around #4. IIRC, that's middle, driver's side cylinder.

If the injectors are easy to swap, i'd swap two around. Reset the codes and drive the car. Does the code come back indicating cylinder #4, or did it move and follow the injector?

If it moves, there's your answer.


EDIT:
Looks like it's a bit of work to get to the injectors under the manifold
http://my.prostreetonline.com/2013/1...-knock-sensor/


One thing I'd check first is compression. I'd check all 6 cylinders and see if they are within 10% of each other. If cyl #4 is low, that could be a cause of the misfire as well.


Basically it's Fuel, spark air and compression. You've checked spark without luck, and i assume the air intake is free from squirrels and other obstructions, so since it's easier, i'd check compression on all 8 cylinders before investigating a fuel issue (with me suspecting a failing injector)

we checked compression on two of the cylinders. #2 and #4, we discovered #2 was a bit low (120) but it could of been a bad reading. #4 was just fine at 180. funny thing is when we were done checking #2 the compression checker was dropped, rendering it useless. (it sits at 30 now -_-) so being i dont want to spend $40 again, I am going to assume compression is just fine.

Guess we will be moving the injectors around. I can also do a resistance test on the injectors if you want. Do you know what the resistance is supposed to be though?

Pretty sure they are high impedence injectors.

I think acceptable range is 11-14.5 ohms


More than likely the solenoids are fine, but they are clogging from age. 200K miles on injectors is a lot.

Injector could be just pizzing a stream of fuel instead of an atomized spray. If you've got spark and all other cylinders are ok, it would seem logical that the injector is faulty.
It is a good, strong blue spark, right?

tested the injectors with a multimeter, they were at 12 ohms so i am assuming the solenoids are fine at least. Most likely what you said, with them getting clogged.

We swapped #2 and #4 around. Want to see if codes follow but after putting everything back together (an hour job :/) car doesnt run for more than a few seconds, hitting the gas keeps it running, but sometimes it makes a squealing noise like the belts are slipping. no CEL either. hooked up my code reader and all i could see in the monitors section was "misfire" "fuel" and "comp" so I am not sure what is going on as of now. Maybe we didnt put in the injectors right but I am pretty sure we did. and yes, we plugged all the cables back in. and all hoses are connected, though we have no coolant (intention was to not run it for more than a minute or so, so no coolant necessary)

here is a video of the current situation. as you can see in decription, video was made quickly, I messed up the first one but you should be able to see what is going on at least...

https://www.youtube.com/watch?v=sqPr...ature=youtu.be


so after you see all of this. WHAT SHOULD I DO? xD i must save my car i need it!

the spark was just as good as the other cylinders.